Re: Music royalties
It amazing how people get intellectual property matters so wrong when there are so many resources available to help them get it right. This "head" of the band is dead wrong on so many levels.
Trademark law nothing do to with drum tracks. Trademarks are business names, slogan, logos, etc. The correct area of law is copyright. And yes, your son has a copyright (legal) interest in the the songs on which he performed. Under the law he is considered a co-author, a co-owner. And unless he has signed away IN WRITING his legal rights in and to those copyrights, there's nothing the "head" of the band can do about.
As far as his compensation, a royalty structure can be set up or the "head" of the band can buy out your son's interests through a copyright assignment agreement, or as it is sometimes called a "sideman" agreement.
There may be other business issues! If your son is a regular member of this band, it may be considered a general partnership under the law, which takes your son's rights and responsibilities to a whole new level. He may have an interest in other assets of the band partnership, like band-owned equipment, the band's name (or trademark), etc.
Good luck...
DS